An unknown ocean: The other rhythms of life

From algae to jellyfish to worms to crustaceans to mollusks to
fish, examples abound of behaviors that change according to moon
and tide. Molecular research is just beginning now, and questions
abound. Raible and Tessmar-Raible's most basic question is how the
lunar clock mechanisms work -- and, indeed, how many different
clock mechanisms there are.

"How many different clocks can you have? It's an open question,"
said Raible. "You can imagine that the inputs could differ between
species. It doesn't have to be light. It could be the pressure of
the water. This is all up for investigation. It's going to be very
interesting to see and compare between species. It may be the same
system, or there may be several independent systems that have
evolved."

Another question is how lunar clocks don't interfere with
circadian clocks, and vice versa. Yet another is whether
land-dwelling creatures still have lunar clocks. It's not uncommon
for complex terrestrial vertebrates to share features with ancient
marine ancestors; in humans, female reproductive cycles correlate
with lunar cycles.

However, Raible and Tessmar-Raible note that many other animals'
reproductive patterns show no connection to the moon, and warn
against speculation.

To them, understanding lunar cycles is less about investigating
potential terrestrial analogues than coming to a deeper
understanding of ocean creatures, which -- despite humanity's
landed perspective -- dominate Earthly life.

"First we want to understand how these things work in organisms
that really have lunar clocks, and see which molecules are
involved," said Tessmar-Raible. "And then, are they really involved
in vertebrates? Do we have them, and what are they doing? Let's
see."